1. Field of the Invention
This invention relates to non-fragmenting, forward-acting pressure relief apparatus used to protect processing equipment, pressure vessels, piping and structures from high pressure events and/or to vent such equipment when destructive and catastrophic overpressures result from any media where an explosion is a risk such as gas and dust particle explosions. Explosion hazards exist in connection with various types of gases and dust particles such as coal, flour, sugar, metal, and plastics. In particular, the invention concerns a single pressure relief rupture disc and composite rupture disc apparatus designed to rupture and vent a protected area, process or equipment whenever an overpressure condition occurs that exceeds a preselected value. The pressure relief rupture disc apparatus incorporates a rupture disc or rupture disc assembly which ruptures and vents an area when overpressure condition or explosion occurs wherein the section of the rupture disc or sections of the rupture disc assembly open fully for pressure relief without fragmentation or separation of the ruptured sections of the disc or composite sections of the disc assembly from the remaining flange portion or portions of the assembly.
The non-fragmenting pressure relief apparatus is adapted for use in a variety of applications including those where cycling between positive and negative pressure in the protected system must be accommodated without rupturing of the disc or disc assembly and opening of the rupturable section of the disc or the rupturable sections of the disc assembly occurs only when a predetermined pressure value is exceeded in the protected zone.
2. Description of the Prior Art
Many industrial processes involve handling and processing of materials that under certain conditions can create hazardous overpressures resulting from explosive conflagrations, or rapid rise in pressure from runaway processes, failure of protective devices such as pressure regulating valves, and similar unpredictable mishaps. Exemplary in this respect are processes involving gases or dust particles in contained vessels or piping which can spontaneously ignite or produce an explosion from untoward events such as a spark or the like and that result in dangerous pressure build-ups within an enclosure, piping or containment vessels. Single rupture discs and composite rupture discs usually having two separate rupture discs have long been employed to protect vessels, pipes, conduits, and structures or areas from overpressure of a predetermined value.
Explosion vents have been provided for many years to cover relief openings in vessels, tanks, bag houses, and piping associated with such equipment, to relieve excess pressure before the excessive pressure damages equipment, components, or structures where the equipment is in operation. Bag houses or the like that are constantly at risk of explosions by virtue of the high concentration of dust within the bag house. Typically bag houses are constructed with one or more pressure relief openings having explosion vents closing each relief opening. The explosion vents seal the openings when the bag houses operate at normal positive or negative pressures and then burst or open when the bag houses are subjected to a pressure build up of a predetermined excess magnitude to uncover the openings and thus vent the interior of the bag houses. To prevent premature or a late bursting, explosion vents must be designed to consistently burst at a particular pressure level. The same type of hazard must also be safely controlled in connection with processing equipment involving combustible gases or dust particles, pipes conveying gases or dust laden fluids from one part of a process to another or to a collection area, processing vessels in which a runaway reaction or untoward build-up of pressure in the vessel can occur without warning, and other industrial processes where an uncontrolled explosion or excessive build-up of pressure is a continuing safety hazard.
Pressure relief apparatus also must accommodate cycling between positive and negative pressure conditions in the equipment, piping, or vessels that require overpressure protection. To this end, it has been conventional to provide rupture disc apparatus in which a rupturable section of the apparatus includes a central bulged area presenting opposed convex concavo surfaces with the concave surface facing the protected zone. This forward acting bulge rupture disc is better able to withstand vacuum conditions within the protected zone than is the case with a flat rupture disc. In addition, pressure relief rupture disc assemblies have included a pair of rupturable central areas with one of the rupture discs being of thicker material than the other rupture disc. In the case of bulged rupture discs, the concavo-convex areas of the discs are in complemental aligned relationship.
Many of the pressure relief devices in the past and present use have been provided with lines of weakness defining the rupturable section of both flat and bulged discs. The lines of weakness are semi-circular in the case of circular discs and rectangular in the instance of rectangular rupture discs. The lines of weakness have been either score lines in one surface of a respective disc defining the rupture area thereof, or a series of elongated slits extending through the rupture disc material with unitary disc webs separating the ends of adjacent elongated slits. Where slits through the disc material are provided defining lines of weakness, a layer of rupturable material, usually a flexible synthetic resin film or the like, is positioned in overlying relationship to the series of slits in order to prevent leakage of fluid therethrough until such time as rupture of the section of the disc defined by the line of weakness occurs. Exemplary pressure relief rupture disc structures in this respect have been provided with two rupture discs in complemental overlying relationship with a layer of flexible material interposed between adjacent surfaces of the rupture discs and an additional strip of flexible material directly overlying a corresponding line of weakness.
The lines of weakness, whether in the form of a score line, or a series of elongated slits defining a line of weakness, do not extend around the entire perimeter of the rupture portion of the disc defined by the line of weakness, but have opposed ends in spaced relationship which present a unitary hinge for the rupturable section of the disc to retain the ruptured portion of the disc with the flange portion thereof, and thereby avoid fragmentation of the disc with attendant released metal fragment hazards in the area surrounding the location of the pressure relief apparatus.
Notwithstanding the provision of anti-fragmentation hinge portions of the rupture discs structures of previous designs, the construction of such hinge areas has not been totally satisfactory to accommodate a multiplicity of overpressure events and conditions. If the width of the hinge area is too great, the pressure value at which the rupturable section gives way is often times compromised resulting in failure of the rupture disc to open at a pre-selected value. On the other hand, if the hinge area is narrowed in order to assure full opening of a rupture disc at a prescribed pressure value, the unitary hinge area tends to also rupture allowing the section of the disc which opens to tear away from the surrounding remaining flange portion of the disc and thereby produce a resultant dangerous metal projectile escaping from the rupture disc assembly at high velocity.
Therefore, there has been and continues to be a need for pressure relief rupture disc apparatus which will reliably open at a preset overpressure value yet is resistant to fragmentation of the ruptured area of the disc upon opening of the disc. It is also desirable that the design of the explosion protection rupture disc assembly be applicable to a wide range of vent openings and different prescribed rupture pressures dependent solely upon materials of construction, thickness of the material and whether the central section is bulged or not, without it being necessary to provide a multiplicity of specifically engineered hinge construction designs in order to prevent fragmentation of the rupturable section of the disc.